1. Field of the Invention
The present invention relates to a suck back valve capable of avoiding, for example, liquid from dripping from a supply port for a pressure fluid by sucking a predetermined amount of the pressure fluid allowed to flow through a fluid passage.
2. Description of the Related Art
A suck back valve has been hitherto used, for example, in the step of producing a semiconductor wafer or the like. The suck back valve functions to avoid so-called liquid dripping which would be otherwise caused such that a minute amount of the coating liquid drips from the supply port to the semiconductor wafer when the supply of the coating liquid to the semiconductor wafer is stopped.
A suck back valve concerning such a conventional technique is shown in FIG. 5 (see Japanese Patent Publication No. 6-47092).
The suck back valve 1 has a main body 5 which is formed with a flow chamber 4 for making communication between an inflow port 2 and an outflow port 3, and a cover 6 which is connected to an upper portion of the main body 5. The inflow port 2 is connected to a supply source (not shown) for a discharge liquid, while the outflow port 3 is connected to an unillustrated nozzle.
An opening 7, which extends in the upward direction, is formed at a substantially central portion of the flow chamber 4. A first diaphragm 8, which partitions the flow chamber 4 at the upper surface in an air-tight manner, is stretched over the opening 7. A vertically movable member 10, which has the lower end allowed to abut against the first diaphragm 8, is arranged in an accommodating chamber 9 which is formed above the first diaphragm 8.
A second diaphragm 11, which is interposed between the main body 5 and the cover 6, is arranged above the vertically movable member 10. The second diaphragm 11 and the vertically movable member 10 are integrally displaceable by the aid of a projection 12 which is caulked to the end of the vertically movable member 10 and which is secured to the second diaphragm 11.
A coil spring 13, which urges the second diaphragm 11 upwardly, is installed between the first diaphragm 8 and the second diaphragm 11. A pressure chamber 15, to which the pilot air is supplied via a pilot air port 14, is formed between the second diaphragm 11 and the cover 6. The cover 6 is provided with a detection unit 17 comprising a detection pin 16 to make abutment against the projection 12 of the vertically movable member 10.
The operation of the suck back valve 1 concerning the conventional technique will be schematically explained below. The pressure of the pressure chamber 15 is high as the pressure is supplied from an unillustrated electropneumatic proportional valve to the pilot air port 14 during the supply of the discharge liquid. The second diaphragm 11 is disposed at the lower position indicated by a two-dot chain line shown in FIG. 5, while resiliently contracting the coil spring 13. The first diaphragm 8, which is operated integrally with the vertically movable member 10, is also disposed at the lower position, and the volume of the flow chamber 4 is decreased.
In such a situation, when the supply source for the discharge liquid is deenergized to stop the discharge from the unillustrated nozzle, then the pilot pressure supplied from the pilot air port 14 is reduced, and the pressure in the pressure chamber 15 is lowered. Therefore, the first diaphragm 8 is moved upwardly integrally with the second diaphragm 11 and the vertically movable member 10 to a state shown by a solid line in FIG. 5. As a result, the first diaphragm 8 is deformed, and the volume of the flow chamber 4 is increased. Accordingly, the discharge liquid contained in the nozzle is sucked.
In this arrangement, the deformation of the first diaphragm 8 corresponds to the vertical movement of the vertically movable member 10, which is detected as the operation of the detection pin 16 of the detection unit 17. A detection signal is derived from the detection unit 17 to an unillustrated instruction unit to perform the feedback control.
However, in the case of the suck back valve 1 concerning the conventional technique as described above, when the displacement amount of the vertically movable member 10 is detected by the aid of the detection pin 16 connected to the detection unit 17, it is difficult to adjust the home position (initial position) of the detection unit 17 because of errors in the attachment position of the first diaphragm 8, for example, due to dispersion of dimensional accuracy concerning individual parts incorporated in the product. Further, the suck back amount is dispersed even when an identical detection signal is obtained, due to dimensional errors caused by the dispersion of the dimensional accuracy.